1. Field of the Invention
The subject invention relates to data integrity in a host computer that has more than one PC card socket and has common signal lines running to the sockets. More particularly, it relates to a method of preventing noise imposed on the signal lines from the insertion or removal of a PC card from corrupting data resulting from transactions with other cards sharing the common signal lines.
2. Description of the Prior Art
The most popular PC card conforms to the PCMCIA (Personal Computer Memory Card International Association) standard which was developed to provide user installed memory and I/O functions for small form factor digital computer systems. The standard specifies a card containing a printed circuit board. This product is usually referred to as a PCMCIA card or a PC card. There are three card formats: Types I, II and III. All three have external dimensions of 54 millimeters by 85.6 millimeters. Thicknesses vary. Type I is 3.3 millimeters thick. Type II is 5 millimeters thick and Type III is 10.5 millimeters thick. The host computer contains one or more sockets into which the PC cards may be inserted. Electrical contact between the host and the PC card is through a 68 pin connector which is also specified by the standard. The PCMCIA standard specifies the function of each of the 68 pins in the connector and supports either an 8 bit or 16 bit bus. There are four ground pins, two power pins and up to 3 free signal pins for additional functions. Communication with the outside world is through an I/O connector which is not specified by the standard.
PCMCIA cards are becoming increasingly popular which has led systems manufacturers to include multiple sockets in the host computer. Typically, in such systems, a unique set of address, data and control signal lines is routed to each PC card socket. However, this is expensive. In an effort to reduce costs, some manufacturers are routing common data, address and some signal lines to all PC card sockets. While less expensive, this design has another problem. When a PC card is inserted or removed, it creates noise on the common signal lines. With the non- shared signal line design, the insertion or removal of a PC card from one socket would not affect transactions occurring simultaneously and involving other PC cards. But if signal lines are shared between multiple sockets, insertion or removal from one socket may cause noise on the common signal lines which may in turn corrupt data resulting from transactions occurring simultaneously through other sockets.
In order to solve this problem, prior art systems required the user to guarantee that no transactions were occurring during PC card insertion or removal. Typically, a LED is provided to alert the user to transactions occurring through other sockets, and therefore an insertion or removal should not be attempted. This approach is however totally dependent on the alertness of the user for its effectiveness.